1. Field of the Invention
The present invention relates to a transverse fan suitable for use as an indoor fan of an air conditioner or the like. In particular the invention relates to a transverse fan capable of reducing air blowing noise and improving air blowing performance achieved by improving blade shapes and blade mounting pitches.
2. Prior Art
FIG. 10 illustrates a common example of an air conditioner incorporated with a transverse fan as an indoor fan. In this air conditioner, suction grills 3 and a blow-out grill 4 are disposed at the upper and the lower portions of the front face 2a of a body casing 2 of an indoor unit 1 as viewed in FIG. 10. The suction grills 3 and the blow-out grill 4 communicate with one another by a ventilation path 6 in a fan casing 5.
In the ventilation path 6, a transverse fan 8, which serves as an indoor fan, is disposed at the downstream side of an indoor heat exchanger 7. Indoor air drawn into the body casing 2 from the suction grills 3 is subjected to heat exchange, after which the cooled or warmed air is blown out through the blow-out grill 4 to the outdoor side by means of the transverse fan 8, thereby cooling or warming the indoor air.
The conventional transverse fan 8 of this type, for example shown in FIG. 11, is provided with, between a pair of left and right disk-shaped side plates 8a and 8b, a plurality of longitudinal vanes 8c, horizontally mounted parallel to the fan axis O in a circumferential direction with predetermined equal pitches (equal distances). Ring-shaped partition plates 8d are disposed in an axial direction of the transverse fan 8 at fixed equal pitches at axially intermediate portions thereof.
The transverse fan 8 constitutes a blower, as shown in FIG. 10, together with the fan casing 5 and a nose 9, and a suction section and a blow-out section are divided at a portion near the two gaps among the nose 9, the fan casing 5 and the transverse fan 8. Particularly, in these two gap sections, because the direction of air flow with respect to the longitudinal blades 8c of the transverse fan 8 is reversed, pressure varies largely, causing air blowing noise.
Such pressure variation produces a noise such that the rotation sounds Pa and Pb having large peaks at a frequency (number of blades x rotation number) of the longitudinal blade 8c of the transverse fan 8 and a frequency of its harmonic sound occurs so as to have waveforms N of FIG. 14A. Because the pressure variation waveforms is steep, this often results in the production of a harmonic wave (harmonic sound Pb) having this wave as the fundamental wave.
FIG. 14A illustrates an analysis of the blower noise N conducted under the conditions that (a) the transverse fan 8 has, for example, a diameter of 88 mm and an overall length of 593 mm, and (b) there are 35 longitudinal blades used, which are disposed parallel to the fan axis O and rotate at a speed of 20 rotations/sec.
Decreasing the size of the gaps between the transverse fan 8 and the nose 9 and between the fan casing 5 and the fan 8 tends to increase the air capacity per rotation. However, since there is an increase in pressure variation in these gap portions, the rotation noise N level becomes higher, which results in an increase in the harmonic component. The air volume of the gaps increases by a larger increment when it is small to a certain extent, so that there is a tendency, when the air volume is the same, for the noise level to decrease and the blowing performance to improve. When the gaps are made too small, however, the rotation noise N level becomes relatively high, thereby producing unpleasant noises. Therefore, the gaps cannot be made too small.
In a blower using the conventional transverse fan 8 in which the longitudinal direction of the longitudinal blades 8c is parallel to the fan axis O direction, the nose 9 and fan casing 5 which form the blower along with the transverse fan 8, are so constructed as being parallel to the fan axis O. Therefore, when each of the longitudinal blades 8c passes near each of the gaps between the fan 8 and the nose 9 and between the fan 8 and the fan casing 5, the whole lengthwise dimension thereof passes at the same time in a short time period, so that pressure variations simultaneously occur in the gaps by an amount corresponding to the length of the longitudinal blades 8c. The total sum of the pressure variations which occur in one longitudinal blade 8c is large. This results in a large distortion in the waveform. Consequently, as shown in FIG. 14A, there is a tendency for harmonic components to occur more frequently. This waveform distortion varies significantly depending on the degree of parallelization of the nose 9, the fan casing 5 and the longitudinal blades 8c, often resulting in a large number of harmonic waves and larger variations in size. In other words, in the blower utilizing the transverse fan 8 in which the longitudinal vanes 8c are arranged such that they are parallel to the fan axis O, a large difference tends to occur among individual units in the harmonic wave component of the rotation noise N. In general, such harmonic waves, which are mixed in with the noise, have a tendency to produce unpleasant noises. When the gaps between the blade 8c and the nose 9 and between the blade 8c and the fan casing 5 are decreased in size to increase the air volume, the rotation noise N level increases considerably, with the result that the gaps cannot be made too small, which prevents the air volume from being increased.
To overcome such problems, there are proposed transverse blades such as disclosed in the Japanese Utility Model Publication No. SHO 59-39196, the Japanese Utility Model Laid-Open No. SHO 56-2092 and the Japanese Utility Model Laid-Open No. SHO 56-45196. Like the transverse fan illustrated in FIG. 12, these conventional fans of the disclosed examples have each of their blades 8f formed not parallel to the fan axis O. This arrangement produces continuous pressure variations in order to reduce the aforementioned rotation noise N level.
Accordingly, in such conventional transverse fans, since the gap between each blade 8f and the nose 9 and between each blade 8f and the fan casing 5 are not parallel to the fan axis O, the pressure variations near these gaps do not occur in the blades 8f as a whole, but are restricted to the smallest regions of the gaps. Therefore, instantaneous pressure variations are small, which results in smaller waveform distortions in this type of fan than in fans in which the blades are formed parallel to the axis. Therefore, as illustrated in FIG. 14B, it is less frequent that harmonic wave component Pb is mixed in the rotation noise N.
Sound pressures are developed in each blade 8f in such a way that continuous phase differences occur in the longitudinal dimension. Therefore, the phase differences are canceled with each other, resulting in a smaller sound pressure sum, so that the fundamental wave of the rotation noise N can be made smaller.
However, since the sound pressure phase differences are produced between a certain distance, it is impossible to completely eliminate the rotation noise N in the entire sound field. In addition, the angle of the blades 8f with respect to the fan axis cannot be made large due to manufacturing reasons. This means that the fundamental wave of the rotation noise N cannot be completely eliminated. Therefore, this rotation noise Pa of this frequency alone appears relatively large. Further, in these transverse fans, the mounting pitches of the blades 8f in the rotating direction must be the same, so that the fundamental wave Pa of the rotation noise N has only a single frequency, with the frequency characteristic of the blowing noise having a large peak value in this frequency. This produces an unpleasant noise. In other words, as illustrated in FIG. 14B, although almost all of the double wave Pb is eliminated, the fundamental wave Pa alone becomes relatively large.
In another conventional transverse fan 8g illustrated in FIG. 13, each blade 8h is formed parallel to the fan axis O and at unequal pitches P in the perimetral dimension, i.e. circumferential direction, of each blade 8h in order to scatter the rotation noise N to eliminate the unpleasant noise. However, as shown in FIG. 14C, due to the reasons described above, the frequency of the harmonic wave component, which has been scattered in the rotation noise N, tends to be produced more often. In addition, there are large differences in the harmonic wave component among individual blades. Therefore, although the frequencies are actually scattered, the harmonic wave component is heard as an unpleasant noise, so that the desired result is not actually achieved by the scattering.
That is, in the above-described two methods, since the rotation noise N can be reduced, the decreasing of the nose gap allows the air volume to be increased slightly, thereby increasing the blowing performance. However, the using of the first method alone causes the rotation noise fundamental wave N to be increased, while the using of the second method alone causes the number of harmonic waves to be increased. Therefore, the nose gap cannot be made small, which limits the improvement of the performance can be improved.